Tin-copper-cadmium electro-plating



Patented Aug. 13, 1957 TlN-COPPER-CADMIUM ELECTRO-PLATING Roy E. Shockley, Kokomo, Ind., assignor to Platalloy Corporation, Kokomo, Ind., a corporation of Indiana N Drawing. Application July 18, 1956, Serial No. 598,535

1 Claim. (Cl. 20444) This invention relates to a method of electro-plating on certain metals. The method involves the plating of tin, copper, and cadmium in one deposit on the metals, wherein the proportions of the three plating metals are maintained within a very definite, predetermined range.

This invention has many quite important objects which include the forming of a finish plating on the metals without a pre-strike, wherein the finish plating comes out with a mirror bright surface; the securing of an extremely dense plate which has long and great endurance particularly where the plated metal is subjected to salt atmospheres or sprays; an extremely intimate bonding, resisting breaking or blistering or separation from the metal carrying the plate; a surprising ease of operation of the process and also of the maintenance of the electrolytic bath; the determination of the composition of plate on the metals in substantially fixed; predetermined proportions as above indicated; and a great saving in cost both in materials and in labor not only in operating the plating process, but also in not requiring the polishing of the plated surface.

At the present time, the invention is successfully employed in electro-plating steel, copper, zinc, brass, bronze, lead, magnesium, and various pot metals including diecast metals of a wide range of compositions. Regardless of the metal to be plated, the same proportions of ingredients in the electrolytic bath and also in the anode are employed.

In practicing the invention, an electrolytic bath is made up to have the following composition in water:

02. per gal. Sodium cyanide 5.5 to 7.5 Sodium hydroxide (or caustic soda) 2.7 to 3.0 Sodium carbonate 0.7 to 1.0

Potassium stanate 10.2 to 12.0

The anode will be made up in particular proportions of the tin, copper and cadmium as they are to be plated on the metals. For each 100 pounds of anode material, block tin, 99 percent plus pure, to the amount of 42 pounds; copper, 99 percent plus pure, to the amount of 52 pounds; and cadmium, commercially pure, to the amount of 6 pounds will be employed. This anode will be previously prepared in the general nature of an alloy. The ratio of anode area to cathode will be one and one half to one. That is these three plating metals will be, at least, so uniformly dispersed throughout the anode that they will be available in the proportions indicated in the plating process.

The electrolyte will be carried in a steel tank, and the tank will be equipped with a heating unit whereby the electrolyte may be maintained within the range of temperatures of 120 degrees F. to 140 degrees F.

The metal which is to receive the plating is previously cleaned by any one of the well known methods, such as is generally employed by those versed in the art, to have the metals present a clean surface, free of grease, and free of oxides.

The metal to be plated, regardless of whether it may be in sheet form, cast form, or other form, is immersed in the bath as the cathode. Upon immersion, the anode also being immersed, the anode and cathode are connected 'into an electric. circuit having the characteristic of providing from 20 to 40 amperes per square foot of cathode surface, with a voltage of from 3 to 3 /2 volts.

In the average plating, there will be deposited a thickness of brightplating of .0001 inch in approximately each 4 minutes. Any thickness up to .0015" to .002" may be had with a bright finish. The metal carrying this deposit of plating is then removed, washed, and dried. It will have a bright, mirror finish without buffing or rubbing.

Referring to the proportions of the ingredients in the electrolytic bath, those proportions are set out as being the critical range in each instance. The preferred weight per gallon of each ingredient is the intermediate weight between the low and the high weight in each instance.

In reference to the range of current applied, the best efficiency is secured within that range, and specifically at 30 amperes per square foot. Likewise the composition of the anode is held within close tolerances of the weights of the individual metals incorporated therein as set forth above. This is required in order that the plate or deposit on the metal being plated will have substantially the same proportions of these three metals embodied in the deposit as controlled by the definite proportions of the ingredients in the bath.

The boric acid will be used in the upper range where the heavier deposit thickness of .002 is desired. However a thickness of over .0005 would seem to meet all requirements. For the thinner deposits, the lower range of boric acid content will be employed. Thus, the boric acid performs a highly desirable function in the alkali bath of insuring a bright finish of the deposit.

The result of this method is extremely surprising in that a single, relatively thin deposit of .0005 inch of the tin, copper, and cadmiun on sheet steel resists a constant spray of salt solution on the plate for a period exceeding 500 hours, all without showing any traces of pitting, rusting, or change in color. Also the deposit is exceedingly resistant to scratching, and even under long periods of constant bending of the metal upon which the deposit appears, there is no separation of the deposit from the metal. In fact the bonding of the deposit to the metal is so intimate that it seems to be an intimate part of the metal itself.

The deposit secured by my process is of such dense, smooth character that, if desired, any subsequent plating deposit, such for example as chromium, precious metals, etc., may be deposited directly thereover.

One of the immediate fields in which this method employable is in the plating of automobile bumpers and the like. At the present time, bumpers are observed to rust within a very few months after the automobile is in use, with the heretofore employed plating of the steel metal constituting the bumpers. These elements in automotive use are subjected to the extremes of calciums, and acids, including those from highway ice removal compositions, and exhaust fumes, and the like, resulting in quick deterioration of that plating. In fact some of these bumpers in use employing the heretofore known methods of plating show that plating not only to be rusted through, but also to be blistered and separated over large areas from the underlying steel.

The present method of plating set out herein provides an extremely thin single deposit which is sutficient to overcome these difliculties encountered, so that in auto motive use, the bumpers may be readily and quickly plated with a great savings of cost in materials as well as in no labor for polishing the finish plated'bumper, but most particularly, an article will be presented to the public which will have a long life, in fact a life as long as that of the average automobile in todays usage. I

While reference has been made to the applying of this invention to automobile bumpers, it is of course equally well adapted to other devices employed not only on automobiles, but throughout the entire field where base metals are to be finished and maintained against corrosion under oxidation, salt atmosphere and the like.

Referring again to the make-up of the bath, sodium cyanide and sodium hydroxide will have to be added from time to time, and potassium stannate, copper cyanide, and cadmium oxide will only be added to make up for what may be dragged outwith the cathode removal. The boric acid will be replenished from time to time as indicated upon a diminishing brightness of the deposit.

I claim:

The method of securing a dense, mirror-bright finish by electro-plating metal articles With an intimately bonded alloy deposit of tin, copper and cadmium, which comprises immersing the article as a cathode in an aqueous solution of from 10.2 to 12.0 ounces of potassium stannate, 1.8 to 2.4 ounces of cuprous cyanide, 0.06 to 0.75 ounce of cadmium oxide, 5.5 to 7.5 ounces of sodium cyanide, 2.7 to 3.0 ounces of sodium hydroxide, and 2.0 to 5.0 ounces of boric acid, each per gallon of water; immersing in the bath as an anode an alloy of tin, copper and cadmium in the same proportions as those like metals of the salts of said bath; and maintaining the temperature of said bath between 120 and 140 degrees F. while passing a plating current between the cathode and the anode.

References Cited in the file of this patent UNITED STATES PATENTS Haines et a1. Nov. 22, 1921 Shockley May 1, 1956 

